System for determining the position of a medical device within a body

ABSTRACT

A system for determining a position of a medical device within a body is provided that reduces positional error by establishing a reference origin closer to the device and/or simplifies the system by integrating components and functions. In one embodiment, a pair of drive electrodes are affixed to opposed surfaces of the body and create a pathway for transmission of current through a position sensor related to the medical device. A pair of reference electrodes proximate the drive electrodes are coupled to a common reference node outputting a reference signal establishing the reference origin. An electronic control unit determines the position of the medical device responsive to the position signal and the reference signal. In another embodiment, a patch affixed to an external surface of the body has a base layer and multiple devices supported on the base layer, electrically isolated from one another, and configured to perform different functions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/981,150, filed 29 Dec. 2010, now pending, which is herebyincorporated by reference as though fully set forth herein.

BACKGROUND OF THE INVENTION

a. Field of the Invention

This invention relates to a system for determining the position of amedical device within a body. In particular, the invention relates to asystem that establishes a reference origin of a position coordinatesystem nearer the medical device to reduce errors in positionmeasurements and that may also simplify the system by integratingcomponents and functions of the system.

b. Background Art

It is desirable to track the position of medical devices as they aremoved within a body so that, for example, drugs and other forms oftreatment are administered at the proper location and medical procedurescan be completed more efficiently and safely. One conventional means totrack the position of medical devices within the body is fluoroscopicimaging. Fluoroscopy is disadvantageous, however, because it subjectsthe patient and clinician to undesirable levels of electromagneticradiation. As a result, medical device navigation systems have beendeveloped to track the position of medical devices within the body.These systems typically rely on the generation of electrical or magneticfields and the detection of induced voltages and currents on positionsensors attached to the medical device and/or external to the body. Theinformation derived from these systems is then provided to a clinicianthrough, for example, a visual display.

One conventional medical device navigation system is offered for saleunder the trademark “ENSITE NAVX™” by St. Jude Medical, Inc. The systemis based on the principal that when electrical currents are passedthrough the thorax a voltage drop occurs across internal organs such asthe heart and this voltage drop can be measured and used to determinethe position of a medical device within the body. The system includesthree pairs of patch electrodes that are placed on opposed surfaces ofthe body (e.g., chest and back, left and right sides of the thorax, andneck and leg) and form generally orthogonal x, y, and z axes as well asa reference electrode that is typically placed near the stomach andprovides a reference value and acts as the origin of the coordinatesystem for the navigation system. Sinusoidal currents are driven througheach pair of patch electrodes and voltage measurements for one or moreelectrodes associated with the medical device are obtained. The measuredvoltages are proportional to the distance of the device electrodes fromthe patch electrodes. The measured voltages are compared to thepotential at the reference electrode and a position of the deviceelectrodes within the coordinate system of the navigation system isdetermined. Referring to FIG. 1, the inventors herein have identified asimplified zero-order circuit 10 that illustrates the system for anygiven axis. Although the following description refers to impedanceswithin circuit 10, only the real or resistive portion of a givenimpedance is used. In the illustrated circuit 10, the medical devicewithin the body includes three electrodes represented by impedances 12₁, 12 ₂, 12 ₃. Amplifiers, filters and other signal processing circuitryfor each electrode create impedances 14 ₁, 14 ₂, 14 ₃. The position ofeach electrode along the axis is determined responsive to the voltage atnodes 16 ₁, 16 ₂, 16 ₃ which, when divided by the drive current, willyield resistances. The resistance generated by the body is representedby resistance 20, denoted as R_(b). The position (P) of an electrodealong an axis may be obtained using the following equation (1):

$P = \frac{S_{f}*R_{b}*R_{i}}{R_{i} + R_{e}}$where R_(e) is the resistance of the individual electrode (typically100-500 ohms, but may exceed 1000 ohms with specialty electrodes), R_(i)is the input resistance of the amplifier (typically 200-1000 kilo ohms),S_(f) is a scale factor (e.g., 25 mm/ohm), and R_(b) is the resistanceof the body along the axis (typically 5-30 ohms).

The above-described system can be used to provide a substantiallyaccurate indication of the position of the medical device. As indicatedin the above-recited formula, however, the position determination alongeach axis is generally proportional to the resistance Rb of the bodybetween the anatomical region of interest and the reference electrode.This resistance Rb varies along each axis. The varying body resistanceRb contributes to a variety of position measurement errors including:(1) drift resulting from a changing position of the medical device overtime relative to the original measured position; (2) shift resultingfrom a change to certain parameters (e.g., connection or disconnectionof the medical device or movement of the reference electrode); (3)scatter resulting from variation of electrode impedances or theamplifiers and related circuitry; and (4) offset resulting fromdifferences in impedance among the electrodes and amplifiers and relatedcircuitry among multiple catheters. For example, in one realisticscenario the body resistance Rb between the location of the referenceelectrode and the anatomical region of interest may be 12 ohms with aninput resistance Ri along the sense amplifier channel of 200 kilo ohmsand a scale factors Sf of 25 mm/ohm. In the case of a specialtyelectrode having a nominal resistance Re of 2 kilo ohms, the resistancemay vary within a range of +/−30%, or between 1.4 and 2.6 kilo ohms. Ifelectrodes having 1.4 and 2.6 kilo ohms are placed at an identicallocation, the position of the electrode along the axis calculated usingequation (1) would yield different results at 297.9 millimeters and296.2 millimeters, respectively—a difference of 1.7 millimeters. In thecase where multiple electrodes are separate by, for example, 5millimeters on a catheter, 1 deviation of 1.7 millimeters about a meanalong any of the three axes will result in a visible error. A linearcatheter may be erroneously depicted with electrode locations creating asaw tooth pattern instead of a smooth pattern. As another example, thebody resistance Rb may change over time due to, for example, a salineinfusion received by a patient which will generally lower bodyresistance. If the initial body resistance Rb is again 12 ohms, a 2%reduction in Rb would change the 297.9 millimeter position location ofthe electrode referred to above to 291.9 millimeters—a 6 millimeterdrift.

The use and placement of the reference electrode is also disadvantageousbecause clinicians are required to locate and place a separate electrodeand facilities must likewise maintain an inventory of the electrodes.Medical device navigation systems employ special purpose electrodes,sensors and other components that are separately connected to the bodysurface. Oftentimes, these systems are used simultaneously with, andeven cooperatively with, other systems employing different electrodesand sensors that are also connected to the body surface. For example,electrocardiography (ECG) electrodes are typically connected to the bodyduring the same procedures in which navigation systems are used in orderto monitor critical vital signs and as an input to the navigation systemto compensate for motion of the heart. Similarly, magnetic navigationsystems typically employ a sensor to monitor movement of the patient inorder to compensate for this movement in determining the position of themedical device. The proliferation of electrodes, sensors and othercomponents connected to the body increases the chance of error insetting up the various systems and increases the time required toprepare and complete a procedure.

The inventors herein have recognized a need for a system for determiningthe position of a medical device within a body that will minimize and/oreliminate one or more of the above-identified deficiencies.

BRIEF SUMMARY OF THE INVENTION

It is desirable to provide a system for determining the position of amedical device within a body. In particular, it is desirable to providea system that will reduce errors in position measurements byestablishing a reference origin for a coordinate system of thepositioning system nearer the medical device to reduce the impact ofbody resistance and/or to simplify the system by integrating componentsand functions of the system.

A system in accordance with one embodiment of the invention fordetermining a position of a medical device within a body, the systemdefining a coordinate system, includes first and second driveelectrodes. The first and second drive electrodes are configured to beaffixed to opposed external surface of the body so as to create a firstpathway for transmission of current through the body and therebygenerate a voltage on a device electrode having a known positionalrelationship to the medical device. The system further includes firstand second reference electrodes disposed proximate the first and seconddrive electrodes, respectively. The first and second referenceelectrodes and coupled to a common reference node. The common referencenode outputs a reference signal establishing an origin of the coordinatesystem. An electronic control unit is configured to determine theposition of the medical device responsive to a position signal generatedby the device electrode and the reference signal.

A system in accordance with the above-described embodiment of thepresent invention is advantageous because it establishes a virtualreference electrode nearer to the medical device and more centrallylocated relative to axes on which currents are transmitted. As a result,body resistance between the medical device and the reference electrodeis reduced or eliminated and measurement position errors resulting fromdrift, shift, scatter and offset are likewise reduced or eliminated.With reference to the example described above, for example, a reductionin the body resistance R_(b) from 12 ohms to 1.2 ohms will cause acorresponding order of magnitude reduction in the potential measurementerrors. Thus, the 1.7 millimeter deviation resulting from the differentresistance values of the electrodes becomes 0.17 millimeters. Similarly,the 6 millimeter drift resulting from variations in body resistance overtime becomes 0.6 millimeters. As a result, the potential errors arebrought within clinically acceptable measures.

A system in accordance with another embodiment of the invention fordetermining a position of a medical device within a body, the systemdefining a coordinate system, includes a field generator and a positionsensor generating a position signal indicative of a position of themedical device in the coordinate system. One of the field generator andthe position sensor is disposed outside of the body and another of thefield generator and the position sensor has a known positionalrelationship to the medical device. The system further includes a patchcomprising a flexible and unitary base layer configured for attachmentto an external surface of the body. The patch further includes a firstdevice supported on the base layer and configured to perform a firstfunction and a second device supported on the base layer and configuredto perform a second function different from the first function. In oneembodiment of the invention, for example, one of the devices comprisesan electrode configured to establish an electrical pathway with anotherelectrode disposed on an opposed surface of the body while the otherdevice comprises an electrode configured to output a reference signalagainst which the position signal is compared. The second device iselectrically isolated from the first device. The system further includesan electronic control unit configured to determine the position of themedical device responsive to the position signal and an output of atleast one of the first and second devices.

A system in accordance with above-described embodiment of the inventionis advantageous relative to conventional systems because it integratescomponent and/or functions that require separate components inconventional systems. As a result, fewer components are required forprocedures thereby reducing inventory and procedural time andcomplexity.

The foregoing and other aspects, features, details, utilities andadvantages of the present invention will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic diagram illustrating resistances in a circuit in aconventional medical position and navigation system.

FIG. 2 is a diagrammatic view of a system in accordance with the presentteachings.

FIG. 3 is a diagrammatic representation of a patch in accordance withone embodiment of the present teachings.

FIG. 4 is a schematic diagram illustrating a circuit coupling drive andreference electrodes to other components of a system in accordance withthe present teachings.

FIG. 5 is a diagrammatic representation of a system in accordance withanother embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring now to the drawings wherein like reference numerals are usedto identify identical components in the various views, FIG. 2illustrates one embodiment of a system 22 for determining the positionof a medical device 24 in a body 26. System 22 may include a pluralityof patch electrodes 28 applied to body 26, an electronic control unit(ECU) 30 and a display 32.

In the illustrated embodiment, system 22 is used to determine theposition of medical device 24 within a heart 34. Medical device 24 may,for example, comprise a deformable catheter of the type used to allowremoval of bodily fluids or injection of fluids and medicine into body26 and/or for transporting surgical tools or instruments within body 16including those use for pacing or tissue ablation of heart 34. Thecatheter may be manipulated manually by a clinician or automaticallythrough, for example, robotic controls and may be inserted within avessel located near the surface of a body (e.g., in an artery or vein inthe leg, neck, or arm) in a conventional manner and maneuvered to aregion of interest in body 26 such as heart 34 under the guidance ofsystem 22. Device 24 may, for example, comprise an electrophysiology(EP) mapping catheter for use in gathering EP data associated with heart34 to enable generation of an image of the geometry of the heart surfaceand related EP data. Device 24 may alternatively comprise anintracardiac echocardiography (ICE) catheter used to generate an imageof a region of interest within body 26 such as heart 34. Device 24 mayalternatively comprise an ablation catheter used to ablate tissue withinheart 34 to treat abnormal heart rhythms such as atrial fibrillation,ventricular tachycardia and similar conditions. Although examples ofspecific medical devices 24 associated with diagnosis and treatment ofconditions associated with heart 34 have been described, it should beunderstood that the inventive system 22 may find application inconnection with determining the position of a variety of medical devicesin varying locations within human and non-human bodies. Medical device24 includes one or more position sensors 36. In the illustratedembodiment, positions sensors 36 are electrodes configured to generatean induced voltage responsive to the transmission of current by patchelectrodes 28.

Patch electrodes 28 are provided to generate electrical signals used indetermining the position of device 24 within a three dimensionalcoordinate system 38 of system 22. Electrodes 28 may also be used togenerate EP data regarding heart 34. Electrodes 28 are placedorthogonally on the surface of body 26 and are used to create axesspecific electric fields within body 26. Electrodes 28 _(X1), 28 _(X2)may be placed along a first (x) axis. Similarly, electrodes 28 _(Y1), 28_(Y2) may be placed along a second (y) axis and electrodes 28 _(Z1), 28_(Z2) may be placed along a third (z) axis. Each of the electrodes 28may be coupled to a multiplex switch 40. ECU 30 is configured throughappropriate software to provide control signals to switch 40 and therebysequentially couple pairs of electrodes 28 to a signal generator 42.Excitation of each pair of electrodes 28 generates an electromagneticfield within body 26 and within an area of interest such as heart 34.Voltage levels at non-excited electrodes 28 may be filtered andconverted and provided to ECU 30 for use as reference values.

Electronic control unit (ECU) 30 provides a means for controlling theoperation of various components of system 22 including device 24,display 32 and switch 40. ECU 30 also provides a means for determiningthe position and orientation of medical device 24. ECU 30 may comprise aprogrammable microprocessor or microcontroller or may comprise anapplication specific integrated circuit (ASIC). ECU 30 may include acentral processing unit (CPU) and an input/output (I/O) interfacethrough which ECU 30 may receive a plurality of input signals includingsignals generated by device 24 (and particularly sensors 36) and patchelectrodes 28 and generate a plurality of output signals including thoseused to control and/or provide data to device 24, display 32, and switch40.

In operation, ECU 30 generates signals to control switch 40 and therebyselectively energize patch electrodes 28. ECU 30 receives positionsignals from position sensors 36 on device 24 reflecting changes involtage levels on sensors 36 and from the non-energized patch electrodes28. ECU 30 uses the raw location data produced by sensors 36 andelectrodes 28 and corrects the data to account for respiration and otherartifacts. ECU 30 then generates display signals to generate a displayon display 32.

Display 32 is provided to convey information to a physician to assist indiagnosis and treatment. Display 32 may comprise a conventional computermonitor or other display device. Display 32 presents a graphical userinterface (GUI) to the physician. The GUI may include a variety ofinformation including, for example, an image of the geometry of heart34, EP data associated with heart 34, graphs illustrating voltage levelsover time for various electrodes, and images of medical device 24 andrelated information indicative of the position of device 24 relative toheart 34 and coordinate system 38.

As discussed hereinabove, conventional position and navigation systemsbased on the principal of passing electric currents through the thoraxusing electrodes 28 and measuring the resulting voltage drops on sensors36 employ a reference electrode that is typically located near thestomach of body 26. The reference electrode serves as the origin ofcoordinate system 38 and the voltage measurements on sensors 36 arecompared to the voltage at the reference electrode. In accordance withone embodiment of the present invention, the reference electrode ismoved to a location on the surface of the body nearer heart 34. In yetanother embodiment of the invention, a virtual reference electrode isestablished within body 26 and, preferably, within heart 34 as describedhereinbelow.

Referring to FIG. 3, in accordance with one embodiment of the invention,at least one of the electrodes—in this case patch electrode 28 _(Z1)—isconfigured to perform multiple functions. In particular, patch electrode28 _(Z1) includes a device 44 comprising an electrode configured toestablish an electrical pathway with another electrode (in this case 28_(Z2)) disposed on an opposed surface of body 26. Electrode 28 _(Z1)also includes a device 46 comprising an electrode configured to act as areference electrode and output a reference signal against which thevoltage measurements on position sensors 36 are compared. Devices 44 and46 are electrically isolated from one another. In the illustratedembodiment, devices 44 and 46 are mechanically connected to one anotherthrough the support of a common flexible base layer with an electricalinsulator 48 separating devices 44 and 46. It should be understood,however, that devices 44 and 46 need not be mechanically connected andcould be mechanically separate with an air gap serving as an insulatorbetween devices 44, 46. In the illustrated embodiment, device 46surrounds device 44 and is concentric with device 44. In this manner,devices 44 and 46 have a common geometric center. It should beunderstood, however, that device 44 may alternatively be arranged tosurround device 46. Further, it should be understood that, whilepreferable, devices 44, 46 need not be arranged so as to be concentricand having a common geometric center and that the benefits of theinvention are achieved by moving the reference electrode (here device46) nearer to heart 34 and the location of positions sensors 36.Accordingly, for example, devices 44, 46 may be arranged to be side byside with their geometric centers offset from one another. Finally,although patch electrode 28 _(Z1) is shown as a multi-function patch inthe illustrated embodiment, it should be understood that any of patches28 _(X1), 28 _(X2), 28 _(Y1), 28 _(Y2), or 28 _(Z2) could be configuredin the same manner.

Referring now to FIG. 4, in accordance with another embodiment of theinvention both of patches 28 _(Z1) and 28 _(Z2) may be configured asmulti-function patches as discussed hereinabove. The devices 46 servingas a reference electrode on each of patches 28 _(Z1) and 28 _(X2) aretied to a common reference node 50. In this manner a virtual referenceelectrode is established within body 26 nearer to heart 34 and positionsensors 36 as opposed to remaining on the surface of body 26. As aresult, the origin of coordinate system 38 to which voltage measurementson sensors 36 are referenced is moved even closer to sensors 36 tofurther reduce position measurement errors. Devices 46 on patches 28_(Z1) and 28 _(Z2) may be tied to reference node 50 through impedancedevices 52, 54, respectively. Impedance devices may comprise a resistoror another conventional impedance device such as a capacitor orinductor. Impedance devices 52, 54 may have the same impedance value.Impedance devices 52, 54 preferably have different impedance values,however, to allow the virtual reference electrode and system origin tobe located at a point other than the geometric center of a lineconnecting devices 46 of patches 28 _(Z1) and 28 _(Z2). The heart 34,for example, is typically located nearer the chest than the back.Accordingly, impedance device 52 may have a lower impedance valuerelative to device 54 to move the virtual reference electrode and systemorigin to a location nearer the chest. In yet another embodiment of theinvention, impedance devices 52, 54 have variable impedance values.Impedance devices 52, 54 may, for example, comprise potentiometers orvariable resistors or rheostats. In this configuration, impedancedevices 52, 54 may be adjusted to establish a reference electrode andsystem origin in an appropriate location despite anatomical differencesamong humans or across species. A method for establishing the virtualreference electrode and system origin may, for example, include thesteps of introducing a medical device 24 with a position sensor 36 intoan anatomical region of interest and adjusting the impedance values ondevices 52, 54 until the difference in voltages generated by positionsensor 36 and output at reference node 50 and is at a predeterminedminimum level such that the location of position sensor 36 isestablished as the virtual reference electrode and system origin.Although the illustrated embodiment shows patches 28 _(Z1) and 28 _(Z2)configured as multi function patches and used to establish the referenceelectrode, it should be understood that patch pairs 28 _(X1) and 28_(X2) or 28 _(Y1) and 28 _(Y2) could alternatively be configured in thesame manner. Further, multiple patch pairs could be configured in thesame manner and collectively or individual (through, e.g., one or moreswitches controlled by ECU 30) to reference node 50 in order toestablish a virtual reference electrode and system origin at a preciselocation along multiple axes.

A system in accordance with the above-identified embodiments of theinvention represents an improvement relative to conventional systems.The inventive system locates the reference electrode serving as theorigin of the navigation system's coordinate system 38 nearer to theanatomical region of interest, such as heart 34, and nearer to theposition sensors 36 on medical device 24. Locating the referenceelectrode in this way reduces or eliminates the impact of the body'sresistance on the position measurements and, particularly, in the interaxis variability of this resistance. Eliminating this resistance resultsin significant improvement in reducing or eliminating measurement errorsdue to drift resulting from a changing position of medical device 24over time relative to the original measured position, shift resultingfrom a changes to certain parameters (e.g., connection or disconnectionof medical device 24 or movement of the reference electrode, scatterresulting from variation of impedance among position sensors 36 andrelated circuitry and offset resulting from differences in impedanceamong the position sensors 36 and related circuitry among differentdevices 24. In the case of scatter for example, and with reference toequation (1) hereinabove, differences in impedance among individualelectrodes will result in different determinations of electrode positioneven if the electrodes are actually located in the same position withinthe coordinate system 38. A reduction in body resistance, however, willcause a proportion reduction in the position values for the twoelectrodes and reduce the overall error in the measured difference inpositions.

As discussed hereinabove, in one embodiment of the invention devices 44,46 are integrated and supported on a common base layer of a patchelectrode 28 affixed to the surface of body 26. Referring to FIG. 5, inanother aspect of the present invention, this concept can be extended topermit the integration of additional or different components andfunctions and use with other types of position and navigation systems.As shown in FIG. 5, a system 56 for determining the position of amedical device 24 within a body 26 in accordance with another embodimentof the invention includes a field generator 58, a position sensor 60, apatch 62 affixed to the surface of body 26 and an electronic controlunit (ECU) 64.

Field generator 58 generates an electrical and/or magnetic field used indetermining the position of device 24 and navigating device 24. Fieldgenerator 58 may comprise an electric field generator as describedhereinabove in system 22 in which electric currents are directed from asignal generator 42 through patch electrodes 28. Alternatively, fieldgenerator 58 may comprise a magnetic field generator such as those inthe systems sold under the trademarks “GMPS™” by Mediguide Ltd. or“CARTO™” by Biosense Webster, Inc.

Position sensor 60 generates a position signal indicative of a positionof medical device 24 in a coordinate system 78 of system 56. Sensor 60may be mounted on device 24. Alternatively, sensor 60 may be physicallyseparate from device 24 and offset from device 24 at a fixed distance.In any event, sensor 60 has a known positional relationship to device 24such that the output of sensor 60 is indicative of the position ofdevice 24. The type of position sensor 60 employed will depend on thetype of field generator 58. If the field generator 58 is an electricfield generator as in system 22, position sensor 60 may comprise aconventional electrode. If the field generator 58 is a magnetic fieldgenerator, position sensor 60 may comprise a conventional coil on whicha current is induced. Sensor 60 will generate a voltage and/or currentthat is indicative of the position of sensor 60 and device 24 andprovide a corresponding position signal to ECU 64. Although positionsensor 60 is shown on or near device 24 in the illustrated embodimentwhile field generator 58 is disposed outside of the body, it should beunderstood that these roles may be reversed with field generator 58within body 26 in a known positional relationship relative to device 24and position sensor 60 disposed outside of body 26.

Patch 62 is used to affix various components of system 56 to body 26 andmay perform a plurality of functions as described below. Patch 62includes a base layer 66 and multiple devices such as devices 68, 70,72, 74 configured to perform different functions and electricallyisolated from one another on patch 62.

Base layer 66 comprises a flexible and unitary structure on whichdevices 68, 70, 72, 74 are supported. Base layer 66 is conventional inthe art and may be made from conventional materials such aspolytetrafluoroethylene (PTFE). Base layer 66 may be made from anelectrically conductive material and may include an adhesive on one sideconfigured to allow base layer 66 to attach and adhere to the externalsurfaces of body 26. Base layer 66 may also include insulationseparating devices 68, 70, 72, 74 from one another to electricallyisolate devices 68, 70, 72, 74.

Devices 68, 70, 72, 74 may be configured to provide a variety offunctions. In accordance with the present invention, one or more ofdevices 68, 70, 72, 74 generate an output that is used by ECU 64together with the position signal generated by position sensor 60 todetermine the position of position sensor 60 and device 24. As discussedhereinabove, devices 68 and 70 may (similar to devices 44, 46) compriseelectrodes configured to establish an electrical pathway with anotherelectrode disposed on an opposed surface of body 26 and configured tooutput a reference signal against which the position signal from sensor60 is compared, respectively. Devices 72, 74 may perform additionalfunctions relied upon in assessing the position of sensor 60 and/orproviding additional information regarding system 22. Device 72, forexample, may comprise an electrode configured to detect electricalactivity in heart 34 (i.e. an ECG electrode). This information can beused to compensate for change s in position of sensor 60 due to movementof heart 34 and/or to provide information regarding electrical activityof heart 34. Device 74 may comprise a position sensor for detectingmovement of body 26. In the case where field generator 58 is a magneticfield generator, for example, device 74 may comprise a coil whose outputis indicative of a change in position of the body within the generatedmagnetic field such as the body position sensor used in the magneticposition and navigation system sold under the trademark “GMPS” byMediguide, Ltd. This information can be used to compensate for change inposition of sensor 60 due to movement of body 26 relative to thegenerated magnetic field.

Although patch 62 is shown in the illustrated embodiment with fourdevices 68, 70, 72, 74, it should be understood that the number and typeof devices employed on patch 62 will depend on the nature of theposition and navigation system employed. For example, patch 62 mayinclude only devices 72, 74 if a magnetic position and navigation systemis used while patch 62 may include devices 68, 70, 72 if a system suchas system 22 is used.

ECU 64 provides a means for controlling the operation of variouscomponents of system 56 including device 24, display 32 and fieldgenerator 58. ECU 64 also provides a means for determining the positionand orientation of medical device 24. ECU 64 may comprise a programmablemicroprocessor or microcontroller or may comprise an applicationspecific integrated circuit (ASIC). ECU 64 may include a centralprocessing unit (CPU) and an input/output (I/O) interface through whichECU 64 may receive a plurality of input signals including signalsgenerated by device 24 (and particularly sensors 60) and devices 68, 70,72, 74 on patch 62 and generate a plurality of output signals includingthose used to control and/or provide data to device 24, display 32, andfield generator 58.

In operation, ECU 64 generates signals to control field generator 58.ECU 64 receives position signals from position sensors 60 on device 24reflecting changes in voltage or current levels on sensors 60 and othersensors within system 56. ECU 64 uses the raw location data produced bysensors 60 and corrects the data to account for respiration and otherartifacts. ECU 64 then generates display signals to generate a displayon display 32.

A system 56 for determining a position of medical device 24 within body26 is advantageous relative to conventional systems because itintegrates component and/or functions that are separate in conventionalsystems. As a result, fewer components are required for proceduresthereby reducing inventory and procedural time and complexity.

Although several embodiments of this invention have been described abovewith a certain degree of particularity, those skilled in the art couldmake numerous alterations to the disclosed embodiments without departingfrom the scope of this invention. All directional references (e.g.,upper, lower, upward, downward, left, right, leftward, rightward, top,bottom, above, below, vertical, horizontal, clockwise andcounterclockwise) are only used for identification purposes to aid thereader's understanding of the present invention, and do not createlimitations, particularly as to the position, orientation, or use of theinvention. Joinder references (e.g., attached, coupled, connected, andthe like) are to be construed broadly and may include intermediatemembers between a connection of elements and relative movement betweenelements. As such, joinder references do not necessarily infer that twoelements are directly connected and in fixed relation to each other. Itis intended that all matter contained in the above description or shownin the accompanying drawings shall be interpreted as illustrative onlyand not as limiting. Changes in detail or structure may be made withoutdeparting from the invention as defined in the appended claims.

What is claimed is:
 1. A system for determining a position of a medicaldevice within a body, said system defining a coordinate system andcomprising: a field generator; a first position sensor generating aposition signal indicative of a three-dimensional position of saidmedical device in said coordinate system, one of said field generatorand said first position sensor disposed outside of said body and anotherof said field generator and said first position sensor having a knownpositional relationship to said medical device; a first patchcomprising: a flexible and unitary base layer configured for attachmentto an external surface of said body; a first device supported on saidbase layer and configured to perform a first function; and a seconddevice supported on said base layer and configured to perform a secondfunction different from said first function, said second deviceelectrically isolated from said first device; a second position sensorcomprising a coil and wherein the first patch is configured to supportthe coil, and wherein the coil is configured such that a current isinduced within the coil when exposed to a magnetic field; and, anelectronic control unit configured to determine said three-dimensionalposition of said medical device responsive to said position signal andan output of at least one of said first and second devices, wherein saidsecond device comprises an electrode configured to establish anelectrical pathway with another electrode disposed on a surface of saidbody.
 2. The system of claim 1, wherein said first device comprises athird position sensor configured to detect movement of said body.
 3. Thesystem of claim 1, wherein said second device comprises an electrodeconfigured to detect electrical activity in a heart of said body.
 4. Thesystem of claim 1, wherein said second device comprises an electrodeconfigured to output a reference signal against which said positionsignal is compared.
 5. The system of claim 1, wherein said patch furtherincludes a third device supported on said base layer and configured toperform a third function different from said first and second functions,said third device electrically isolated from said first and seconddevices.
 6. The system of claim 1, wherein one of said first and seconddevices surrounds another of said first and second devices.
 7. Thesystem of claim 6, wherein said first and second devices areconcentrically arranged.
 8. The system of claim 1, wherein a geometriccenter of said first device is offset from a geometric center of saidsecond device.
 9. The system of claim 1, further comprising an impedancedevice coupled to the first patch, the impedance device configured toallow the electronic control unit to create a virtual referenceelectrode at a desired distance from the first patch.
 10. A system fordetermining a position of a medical device within a body, said systemdefining a coordinate system and comprising: a field generator; a firstposition sensor generating a position signal indicative of athree-dimensional position of said medical device in said coordinatesystem, one of said field generator and said first position sensordisposed outside of said body and another of said field generator andsaid first position sensor having a known positional relationship tosaid medical device; a patch electrode comprising: a flexible base layerconfigured for attachment to an external surface of said body; a firstelectrode supported on said base layer, said first electrode configuredto generate an electrical signal; and, a second electrode supported onsaid base layer, said second electrode configured to establish an originof the coordinate system and to generate a reference signal; a secondposition sensor comprising a coil and wherein the coil is configured tocouple to the patch electrode, and wherein the coil is configured suchthat a current is induced within the coil when exposed to a magneticfield; and, an electronic control unit configured to determine saidthree-dimensional position of said medical device responsive to saidposition signal and said reference signal.
 11. A system for determininga position of a medical device within a body, said system defining acoordinate system and comprising: a field generator; a first positionsensor generating a position signal indicative of a three-dimensionalposition of said medical device in said coordinate system, one of saidfield generator and said first position sensor disposed outside of saidbody and another of said field generator and said first position sensorhaving a known positional relationship to said medical device; a patchelectrode comprising: a flexible base layer configured for attachment toan external surface of said body; a first electrode supported on saidbase layer and configured to establish an electrical pathway withanother electrode disposed on a second external surface of the bodyopposite the first external surface and to generate an electric fieldwithin the body; and, a second position sensor comprising a coil andwherein the coil is configured to couple to the patch electrode, andwherein the coil is configured such that a current is induced within thecoil when exposed to a magnetic field; and, an electronic control unitconfigured to determine said three-dimensional position of said medicaldevice responsive to said position signal and said reference signal. 12.The system of claim 11, wherein said base layer includes an adhesive ona first side configured for coupling to said first surface of said body.13. The system of claim 11, wherein said base layer is unitary inconstruction.
 14. The system of claim 11, further comprising a secondelectrode and wherein said first and second electrodes are electricallyisolated from one another.
 15. The system of claim 11, furthercomprising a second electrode and wherein one of said first and secondelectrodes surrounds another of said first and second electrodes. 16.The system of claim 15, wherein said first and second electrodes areconcentrically arranged.
 17. The system of claim 11, further comprisinga second electrode and wherein a geometric center of said firstelectrode is offset from a geometric center of said second electrode.18. The system of claim 11, further comprising a second position sensorsupported on said base layer, said position sensor configured to detectmovement of the body.